Hydatid disease, also known as echinococcosis, is a parasitic illness caused by the larvae of the Echinococcus granulosus tapeworm. The disease is characterized by the formation of fluid-filled cysts in various parts of the body, most commonly the liver and lungs. Some synonyms for hydatid disease include cystic echinococcosis, unilocular hydatid cyst, and unilocular cystic disease. Other related terms may include alveolar echinococcosis, which is caused by a different species of tapeworm and results in more aggressive cyst growth, and polycystic echinococcosis, which involves the development of multiple cysts throughout the body. Treatment for hydatid disease typically involves surgical removal of cysts and antiparasitic medication to prevent reinfection.